Add functionality to allow for mutated events be stored by the backend and changes reflected on the webUI

[lspxxv]

A customer requested the functionality to mutate keepalive events to change their statuses. On testing and with code confirmation, we've found that the mutated events are only used/processed by the handler and do not persist on the backend.

Feature Suggestion

Possible Implementation

Context

Context - https://secure.helpscout.net/conversation/2131190251/30734?folderId=4465878
Code -

sensu-go/backend/pipeline/adapterv1.go

Line 202 in 124efef

mutatedData, err := a.processMutator(ctx, workflow.Mutator, event)

[asachs01]

Let's restate this--with Swisscom, they want to change the keepalive status. Rather than mutating, maybe a separate config parameter would be the real ask? Doing event pre-processing would introduce a bottleneck that could be catastrophic.